Castle nut is a locking device in which__________________?

A. one smaller nut is tightened over main nut and main nut tightened against smaller one by loosening, creating friction jamming
B. a slot is cut partly is middle of nut and then slot reduced by tightening a screw
C. a hard fiber or nylon cotter is recessed in the nut and becomes threaded as the nut is screwed on the bolt causing a tight grip
D. through slots are made at top and a cotter is passed through these and a hole in the bolt, and cotter spitted and bent in reverse direction at other end
E. none of the above.